Multi-chip land grid array carrier

ABSTRACT

A land grid array (LGA) carrier includes an interposer having a first surface and a second surface opposite the first surface, with a plurality of locations on the first surface adapted to receive a plurality of semiconductor dice and passive components. The second surface has a plurality of conductive pads coupled thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to chip carriers, and more specifically,to a multi-chip land grid array carrier.

2. Description of Related Art

Computer processors include various cache memories, including memorycaches and disk caches. A memory cache is a portion of memory made ofhigh-speed static random access memory (SRAM) instead of the slower andcheaper dynamic RAM (DRAM) used for main memory. Memory caching iseffective because most programs access the same data or instructionsover and over. By keeping as much of this information as possible inSRAM, the computer avoids accessing the slower DRAM.

Some memory caches are built into the architecture of microprocessors.Such internal caches are often called primary, or Level 1 (L1) caches.Many computers also come with external cache memory, called Level 2 (L2)caches. The L2 cache is coupled to a dedicated bus, sometimes referredto as a "backside bus." Like L1 caches, L2 caches are composed of SRAMbut they are typically much larger. The L2 cache improves system-levelperformance by improving the processor's memory read and writeperformance, as well as decreasing the system bus utilization. The largeL2 cache results in less processor read requirements to main memory,thereby reducing the number of times the processor needs to access thesystem bus.

For example, the Intel® Pentium® Pro processor package includes themicroprocessor chip and an L2 cache die packaged in a single package.The microprocessor chip and the L2 cache memory die are both mounted ina dual-cavity microprocessor package. The microprocessor package maythen be mounted on a system motherboard. The tight coupling of themicroprocessor chip and the L2 cache improves system performance andefficiency. The Pentium® Pro processor architecture is described in theIntel Architecture Software Developer's Manual, Volume 1: BasicArchitecture, 1996/1997, available from Intel® Corporation, and inPentium® Pro Processor System Architecture, Mindshare, Inc., 1997, bothof which are incorporated by reference herein in their entirety.

While cache devices are often implemented using multiple memory chips, adesign such as the Pentium® Pro L2 cache comprises a single die. Thesize of the L2 cache varies according to various models of the Pentium®Pro available. For example, the processor may be implemented with 256KB, 512 KB, 1MB, etc. of L2 cache capacity. Manufacturing the single,large memory die for the L2 cache may be difficult and expensive.Defects in a single-die L2 cache may not be discoverable until after theprocessor and L2 cache die are assembled into their shared package. If adefect is found in the L2 cache after it is assembled into themicroprocessor package, the entire package often must be scrapped. Thus,it may be desirable to implement the L2 cache in a manner that allowsadditional flexibility and simplifies manufacturing and testing.

Mounting the cache memory chips directly to a motherboard, as in manyprior art cache implementations, greatly reduces performance. With cachememory implemented on the motherboard, each semiconductor die comprisingthe memory device is typically mounted in a conventional single-diepackage. The single-die packages are then soldered directly to themotherboard or mounted in sockets. The speed at which the cache runs issignificantly slower when implemented on the motherboard.

In a compromise solution, single-die memory devices are coupled to adaughterboard along with the microprocessor. The daughterboard is thenplugged into the motherboard. While this cache implementation improvesperformance over directly mounting the cache memory packages on themotherboard, it requires a larger footprint since the cache comprisesseveral conventional single-die packages. Moreover, the daughterboardimplementation still operates at a significantly slower speed than anintegrated L2 cache. In one prior art daughterboard L2 cacheimplementation, the L2 cache operates at only half the speed of theprocessor.

Rather than using several single-die memory devices for an L2 cache,several semiconductor dies could be directly mounted in a processorpackage using conventional methods, such as controlled collapse chipconnection (C4). This also has drawbacks. For example, the memory devicesemiconductor die may not be tested until mounted along with themicroprocessor chip. If a single memory chip is defective, the entiremicroprocessor package must be scrapped, as removing and replacing asingle semiconductor die is, at best, very difficult if not impossible.

The present invention addresses some of the above mentioned and otherproblems of the prior art.

SUMMARY OF THE INVENTION

In one aspect of the invention, a land grid array (LGA) carrier includesan interposer having a first surface and a second surface opposite thefirst surface, with a plurality of locations on the first surfaceadapted to receive a plurality of semiconductor dies and passivecomponents. The second surface has a plurality of conductive padscoupled thereto.

In another aspect of the invention a method of assembling a multi-chipdevice includes fabricating an interposer having a first surface and asecond surface and populating the second surface with a plurality ofconductive pads. A solder ball is coupled to each of predefinedconductive pads, and a plurality of semiconductor dies and a pluralityof passive devices are coupled to the first surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is a plan view of a first surface of a multi-chip land grid array(LGA) carrier in accordance with an embodiment of the invention;

FIG. 2 is an end view of the multi-chip LGA carrier of FIG. 1;

FIG. 3 is a plan view illustrating the bottom portion of an embodimentof the LGA chip carrier in accordance with the invention;

FIG. 4 is a partial plan view showing a portion of the bottom portion ofan embodiment of the LGA chip carrier in accordance with the invention,illustrating solder balls coupled to some of the conductive pads;

FIG. 5 is a partial end view of the embodiment illustrated in FIG. 4;and

FIG. 6 is a plan view illustrating an embodiment of an LGA carrier inaccordance with the invention, coupled to a substrate with a single chippackage.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

FIG. 1 is a plan view and FIG. 2 is an end view illustrating anexemplary land grid array (LGA) carrier 10 in accordance with anembodiment of the invention. The LGA carrier 10 includes an interposer12, which in one embodiment of the invention is fabricated out oforganic advanced circuit board material, as is known in the art. Theinterposer provides a substrate to which electronic components arecoupled, thus acting as a multi-chip subassembly in a multi-chippackage. The top surface 13 of the interposer 12 includes a firstportion 14 that is adapted to receive a plurality of semiconductor dies16 and passive components 18, such as capacitors, resistors andinductors. The semiconductor dies 16 may be coupled to the first portion14 using controlled collapse chip connection (C4), as is known in theart. Other methods of coupling the semiconductor dies 16 may also beemployed.

The interposer 12 may include a second portion 20 located about theperiphery of the interposer 12 top surface 13. Particular embodiments ofthe interposer 12 employ the second portion 20 to provide a "handlingarea," supplying adequate space for assembly machines, such as automatedpick-and-place devices, to handle the interposer 12. In one embodiment,the second portion 20 is about 5 to 7 mm wide (reference 22).

The interposer 12 further includes a bottom surface 24 that has aplurality of conductive pads 26 coupled thereto. A plurality ofconductive traces (not shown) are placed within the interposer 12 in apredefined manner to route power, signals, etc. to the components 16, 18and electrically couple the various components 16, 18 together. Theconductive traces also selectively couple the components 16, 18 to aplurality of vias 28, which in turn, couple the components 16, 18 to atleast some of the conductive pads 26.

FIG. 3 illustrates the bottom surface 24 of an embodiment of theinterposer 12 in accordance with the present invention. In theembodiment of the interposer 12 illustrated in FIG. 3, the plurality ofconductive pads 26 cover essentially the entire bottom surface 24. Inthe embodiment of FIG. 3, the conductive pads 26 are arranged in anarray of rows and columns, though alternate arrangements may be used. Inone embodiment, the array of conductive pads 26 includes 41 rows and 27columns, while in another embodiment, the array includes 41 rows and 45columns. Thus, the bottom surface 24 may include over 1,800 conductivepads. Some of the conductive pads 26 are coupled to the vias 28, in turncoupling the conductive pads 26 to the components 16, 18 on the topsurface 13, while other conductive pads 26 are not coupled to the vias28.

FIG. 4 is a partial plan view of the bottom surface 24, and FIG. 5 is apartial end view of the interposer 12 of an embodiment of the invention.The conductive pads 26 that are electrically coupled to the components16, 18 on the top surface 13 of the interposer 12 have a solder ball 30attached thereto for coupling the interposer 12 to a surface of anothersubstrate (not shown) or other device. Alternatively, the conductivepads 26 that are electrically coupled to the components 16, 18 may havepins (not shown) attached thereto for coupling the interposer 12 to thesubstrate or other device.

Moreover, the conductive pads 26 that are not coupled to the components16, 18 on the top surface 13 do not have a solder ball 30 attachedthereto. Thus, essentially the entire bottom surface 24 of theinterposer 12 may be populated with conductive pads 26, but onlypreselected conductive pads 26 have a solder ball 30 coupled thereto. Inother words, this embodiment of the present invention provides a large,ball grid array (BGA) device that includes unused pads 26 on the bottomsurface 24. Pads that are unused in the specific device do not havesolder balls attached thereto. This adds flexibility in design andrework of specific embodiments of the LGA carrier 10. Still further, inone embodiment, only a preselected portion of the conductive pads 26having solder balls 30 coupled thereto are tested during themanufacturing process, additionally reducing manufacturing costs.

FIG. 6 is a plan view, illustrating an embodiment of an LGA carrier 10,in accordance with an embodiment of the invention, coupled to anothersubstrate 50, along with a single-chip device 52. The interposer 12includes a plurality of semiconductor dies 16 and passive devices 18coupled to the interposer 12. In one embodiment, the single-chip device52 comprises a microprocessor device, and the semiconductor dies 16comprise memory chips that function as an L2 cache of the microprocessordevice. The passive components 18 may include capacitors, resistors andinductors arranged as filters to facilitate high-speed device operation.Thus, the interposer acts as a multi-chip subassembly in a multi-chippackage. In FIG. 6, the interposer 12 is shown having four semiconductordice 16 coupled thereto, though other arrangements, including differentquantities of semiconductor dice, are envisioned.

Coupling the semiconductor dies 16 to the interposer 12, as illustratedin FIG. 6, rather than coupling the semiconductor dies 16 directly tothe substrate 50, allows pretesting of the semiconductor dies 16. Forexample, if the semiconductor dies 16 comprise memory chips of amicroprocessor L2 cache, the memory chips may be tested "at speed" priorto being coupled to the substrate 50, along with the microprocessordevice 52. If the pretesting discovers defects, the LGA carrier 10 maybe reworked or scrapped prior to coupling the interposer 12 to thesubstrate 50. The LGA carrier 10 allows simpler attachment of multiplesemiconductor dies 16 to the substrate 50. Once the LGA carrier 10multi-chip subassembly is implemented in a multi-chip assembly, as inFIG. 6, the multiple semiconductor dies 16 may be simultaneously removedfrom the substrate 50 of defective assemblies, if necessary.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

What is claimed is:
 1. A land grid array (LGA) carrier, comprising:aninterposer having a first surface and a second surface opposite thefirst surface; a plurality of locations on the first surface adapted toreceive a plurality of semiconductor dies and passive components,wherein the passive components are selected from a group comprisingresistors, capacitors, and inductors; and, a plurality of conductivepads coupled to the second surface and electrically coupled withselected ones of the semiconductor dies and passive components.
 2. TheLGA carrier of claim 1 further comprising a plurality of solder balls,wherein at least some of the conductive pads have one of the solderballs attached thereto.
 3. The LGA carrier of claim 1 further comprisinga plurality of pins, wherein at least some of the conductive pads haveone of the pins attached thereto.
 4. The LGA carrier of claim 1, whereinthe interposer is fabricated out of an organic material.
 5. The LGAcarrier of claim 1 further comprising a plurality of conductive tracesin the interposer arranged to electrically couple the locations in apredefined manner, the conductive traces further electrically coupled toat least some of the conductive pads.
 6. The LGA carrier of claim 5wherein at least some of the conductive pads do not have conductivetraces electrically coupled thereto.
 7. The LGA carrier of claim 1,wherein the conductive pads are configured in an array of rows andcolumns.
 8. The LGA carrier of claim 7 wherein the array comprises atleast 40 rows and at least 45 columns.
 9. The LGA carrier of claim 8wherein the plurality of conductive pads comprises at least 1,800conductive pads.
 10. The LGA carrier of claim 8 wherein the array ofconductive pads covers essentially the entire second surface.
 11. TheLGA carrier of claim 1 wherein the first surface comprises first andsecond portions, wherein the first portion is adapted to receive theplurality of semiconductor dies and passive components.
 12. The LGAcarrier of claim 11 wherein the second portion is located about theperiphery of the first surface, generally surrounding the first portion.13. The LGA carrier of claim 12 wherein the second portion is notadapted to receive the semiconductor dies and passive components. 14.The LGA carrier of claim 1 further comprising a plurality ofsemiconductor dies coupled to the first surface.
 15. The LGA carrier of14 wherein at least one of the plurality of semiconductor dies comprisesa memory chip.
 16. The LGA carrier of claim 14 wherein at least one ofthe plurality of semiconductor dies is coupled to the first portionusing controlled collapse chip connection (C4).
 17. The LGA carrier ofclaim 14 further comprising a plurality of passive components coupled tothe first surface.